Alexis Alvey, Horticulture Agent, CSU Denver Extension
I have always loved trees and I’m sure that many of you gardeners out there feel the same why. I have always been enchanted by the beauty and power that they convey, their leafy greenness and tall trunks reaching up towards the sky. I could go on, but I won’t since I know that I’m preaching to the choir. Shockingly, there are some folks out there who don’t feel the same way and who don’t like trees (insert audible gasp here)! Perhaps with a little more convincing, we can get more people to understand the need for trees so that our city officials can make the correct decisions about our urban forest. So here are some awesome and quantifiable benefits of having trees in our cities:
- According to a study by the US Forest Service that evaluated the benefits of community trees, for every dollar that a city invests in a community tree program, trees will give back $1 - $2 in environmental benefits.
- Shaded streets are 10-40 degrees Fahrenheit cooler since paved areas store about half the sun’s energy. Tree evapotranspiration accounts for an important percent of this cooling effect.
- A well-placed tree can reduce home cooling costs by 10-30%. In summer, trees block 70-90% of the sun’s radiation on a sunny day. Plant trees so that they can shade air-conditioning units and west-facing walls.
- Trees improve air quality by removing ozone, particulate matter, nitrogen dioxide, sulfur dioxide, and carbon monoxide. The Forest Service’s UFORE model estimates 1200 – 1800 tons of atmospheric contaminants are removed annually in a major city in thee US by their urban forest.
- One tree can absorb the same amount of carbon in a year that a car produces while driving 26,000 miles.
- A large percentage of paved surfaces in cities can contribute to flash flooding in storm events. By intercepting precipitation, trees reduce the speed and quantity of raindrops hitting the ground. One study found that in a city with a tree canopy cover of 22%, runoff was reduced by 7% by those trees. There is also a reduced cost in constructing stormwater retention ponds.
So that’s quite a lot of environmental benefits that trees provide! But did you know that trees also provide psychological and social benefits as well? Nature has a restorative and calming effect on human beings. (If you want to look deeper into this subject, take a gander at Richard Louv’s book, Last Child in the Woods.) Some social benefits of trees include:
- A landmark study conducted in the mid ‘80s found that hospital patients recovering from abdominal surgery who had a view of a wooded scene vs a brick wall out their windows recovered more quickly, required less pain medication, and had fewer complications. Postoperative hospitalization was reduced by 8.5%.
- A study in 2001 found fewer violent and property crimes occurred in areas of dense trees and grass. The authors concluded that plants may mitigate the psychological precursors to crime, such as irritability, inattentiveness, and impulsive behavior. Landscape plants may increase the perception of safety of inner-city residents by providing an open and inviting place to congregate.
- A study in Massachusetts found that trees added 5-15% to the sale price of hypothetical homes on lots with and without trees.
- The US Forest Service reports that consumers spend 12% more for goods and services in tree-lined business districts. Visitors also tend to shop more frequently, stay longer, and spend more for parking.
Trees are really great with all their environmental, psychological, and social benefits! If you want to find out how much in benefits your tree is providing, check out the National Tree Benefit Calculator at www.treebenefits.com. For instance, the calculator estimates that a 14 inch Kentucky Coffee Tree gives back $100 per year in benefits. Pretty frickin’ awesome!!!